1. Field of the Invention
The present invention relates to a manufacturing technique of helical parts, typically exemplified by coil springs or the like.
2. Description of the Related Art
Conventionally, a spring has been manufactured by helically winding a wire by a spring manufacturing apparatus which serves as a helical part manufacturing apparatus, and then both ends of the spring are processed into flat surfaces with the use of a grinding machine which is provided differently from the spring manufacturing apparatus. The necessity of the differently provided grinding machine has been causing problems in terms of costs and machine installing locations. Also, the grinding process necessary in addition to the spring manufacturing process has been causing reduced production efficiency.
In order to solve the problems, the conventional techniques have proposed to push the wire fed out by a feed roller against a tool and helically wind the fed wire, thereafter irradiate a laser beam from the outer circumference of the helicoid for cutting the wire, or emit jet water for cutting the wire (refer to Japanese Patent No. 2004851 (U.S. Pat. No. 5,285,669) and Japanese Patent No. 3854242).
Furthermore, a discoid grindstone is commercially available these days as a grindstone that can be used in board material cutting machines. The discoid grindstone can precisely cut hard and brittle materials such as extremely hard alloy and glass, magnetic materials such as ferrite, and other hard-to-grind composite materials. The discoid grindstone has 50 to 300 mm in external diameter, 0.5 to 1.0 mm in thickness, and has a diamond grain abrasive coating layer on the outer circumferential portion of the highly rigid alloy (refer to http://www.heiwa-tec.co.jp).
Furthermore, according to http://www.discousa.com/jp/products/catalog/index.html, a discoid dicing (cutting) blade having 0.1 to 0.4 mm in thickness which is fit to realize precise cutting of semiconductor integrated circuits, glass, ceramics, ferrite and the like is commercially available.
Hereinafter, a method of cutting a wire using a conventional spring manufacturing apparatus is described with reference to FIG. 19.
The conventional spring manufacturing apparatus in FIG. 19 strikes the wire W, which is pushed out of the guide 11, against the pointing tool 21 to helically wind the wire W, and cuts the wire W with the cutting tool 23 which is slidable in vertical directions and the mandrel 24 which provides shear force to the wire W in cooperation with the cutting tool 23.
Next described with reference to FIGS. 20 to 26A and 26B is a processing method for flattening both ends of a spring by a conventional grinding machine.
As mentioned above, when a spring is manufactured by a conventional spring manufacturing apparatus, since the end portion 5a of the wire W helically wound is cut off in the radial direction as shown in FIGS. 23A and 23B, the surfaces of both end portions of the spring do not become flat.
Therefore, both end portions of the spring 5 are ground to be flat surfaces in a manner that the spring is sandwiched between the rotating grindstones 131 as shown in FIGS. 20 to 22.
FIGS. 24A and 24B show the shape of spring 5 in which the circumferences of the end portions are ideally ground. The end portions of the spring have ultra-thin portions W1 which are formed at the tip of the wire W when ground. In order to prevent the ultra-thin portions W1 from snapping and falling at the time of use, the ultra-thin portions W1 are cut off as shown in FIGS. 25A and 25B after the grinding process. It would be ideal that a grinding amount of the end portions is about the same size as the wire diameter as shown in FIGS. 24A and 24B. However, if the grinding amount of the end portions becomes less than the wire diameter, as shown in FIGS. 26A and 26B it is possible to obtain a similar shape as the spring whose both end portions are cut off. In this case, the sectional area of the end portion 5b is slightly smaller than the sectional area of the ideal end portion 5a (i.e., since the spring has a larger surface of ungrounded rounded portion, the posture of the spring becomes unstable when the end portion is set vertically).
However, according to aforementioned Japanese Patent No. 2004851, there is a disadvantage in that using a laser beam causes thermal deformation on the cutting surface.
Furthermore, according to Japanese Patent No. 3854242, since extra-high-pressure jet water is emitted, safety measures on the periphery are necessary. Moreover, a disadvantage arises when the jet water that strikes the wire splashes and exerts damaging effects on the spring as a completed product and other parts of the apparatus.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention as follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.